Cabletron Systems FDDI TECHNOLOGY GUIDE

Transcription

1 Cabletron Systems FDDI TECHNOLOGY GUIDE

2 NOTICE Cabletron Systems reserves the right to make changes in specifications and other information contained in this document without prior notice. The reader should in all cases consult Cabletron Systems to determine whether any such changes have been made. The hardware, firmware, or software described in this manual is subject to change without notice. IN NO EVENT SHALL CABLETRON SYSTEMS BE LIABLE FOR ANY INCIDENTAL, INDIRECT, SPECIAL, OR CONSEQUENTIAL DAMAGES WHATSOEVER (INCLUDING BUT NOT LIMITED TO LOST PROFITS) ARISING OUT OF OR RELATED TO THIS MANUAL OR THE INFORMATION CONTAINED IN IT, EVEN IF CABLETRON SYSTEMS HAS BEEN ADVISED OF, KNOWN, OR SHOULD HAVE KNOWN, THE POSSIBILITY OF SUCH DAMAGES. Copyright 1996 by Cabletron Systems, Inc., P.O. Box 5005, Rochester, NH All Rights Reserved Printed in the United States of America Order Number: April 1996 SPECTRUM, LANVIEW, Remote LANVIEW NCM-PCMMAC, MicroMMAC, and BRIM are registered trademarks and Element Manager, EPIM, EPIM-A, EPIM-F1, EPIM-F2, EPIM-F3, EPIM-T, EPIM-X, FOT-F, FOT-F3, HubSTACK, SEH, SEHI, and TMS-3 are trademarks of Cabletron Systems, Inc. All other product names mentioned in this manual may be trademarks or registered trademarks of their respective companies. Printed on Recycled Paper FDDI Technology Manual i

3 Notice FCC NOTICE This device complies with Part 15 of the FCC rules. Operation is subject to the following two conditions: (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation. NOTE: This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to Part 15 of the FCC rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This equipment uses, generates, and can radiate radio frequency energy and if not installed in accordance with the operator s manual, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause interference in which case the user will be required to correct the interference at his own expense. WARNING: Changes or modifications made to this device which are not expressly approved by the party responsible for compliance could void the user s authority to operate the equipment. DOC NOTICE This digital apparatus does not exceed the Class A limits for radio noise emissions from digital apparatus set out in the Radio Interference Regulations of the Canadian Department of Communications. Le présent appareil numérique n émet pas de bruits radioélectriques dépassant les limites applicables aux appareils numériques de la class A prescrites dans le Règlement sur le brouillage radioélectrique édicté par le ministère des Communications du Canada. VCCI NOTICE This equipment is in the 1st Class Category (information equipment to be used in commercial and/or industrial areas) and conforms to the standards set by the Voluntary Control Council for Interference by Information Technology Equipment (VCCI) aimed at preventing radio interference in commercial and/or industrial areas. Consequently, when used in a residential area or in an adjacent area thereto, radio interference may be caused to radios and TV receivers, etc. Read the instructions for correct handling. ii FDDI Technology Manual

4 Notice CABLETRON SYSTEMS, INC. PROGRAM LICENSE AGREEMENT IMPORTANT: Before utilizing this product, carefully read this License Agreement. This document is an agreement between you, the end user, and Cabletron Systems, Inc. ( Cabletron ) that sets forth your rights and obligations with respect to the Cabletron software program (the Program ) contained in this package. The Program may be contained in firmware, chips or other media. BY UTILIZING THE ENCLOSED PRODUCT, YOU ARE AGREEING TO BECOME BOUND BY THE TERMS OF THIS AGREEMENT, WHICH INCLUDES THE LICENSE AND THE LIMITATION OF WARRANTY AND DISCLAIMER OF LIABILITY. IF YOU DO NOT AGREE TO THE TERMS OF THIS AGREEMENT, PROMPTLY RETURN THE UNUSED PRODUCT TO THE PLACE OF PURCHASE FOR A FULL REFUND. CABLETRON SOFTWARE PROGRAM LICENSE 1. LICENSE. You have the right to use only the one (1) copy of the Program provided in this package subject to the terms and conditions of this License Agreement. You may not copy, reproduce or transmit any part of the Program except as permitted by the Copyright Act of the United States or as authorized in writing by Cabletron. 2. OTHER RESTRICTIONS. You may not reverse engineer, decompile, or disassemble the Program. 3. APPLICABLE LAW. This License Agreement shall be interpreted and governed under the laws and in the state and federal courts of New Hampshire. You accept the personal jurisdiction and venue of the New Hampshire courts. EXCLUSION OF WARRANTY AND DISCLAIMER OF LIABILITY 1. EXCLUSION OF WARRANTY. Except as may be specifically provided by Cabletron in writing, Cabletron makes no warranty, expressed or implied, concerning the Program (including its documentation and media). CABLETRON DISCLAIMS ALL WARRANTIES, OTHER THAN THOSE SUPPLIED TO YOU BY CABLETRON IN WRITING, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, WITH RESPECT TO THE PROGRAM, THE ACCOMPANYING WRITTEN MATERIALS, AND ANY ACCOMPANYING HARDWARE. 2. NO LIABILITY FOR CONSEQUENTIAL DAMAGES. IN NO EVENT SHALL CABLETRON OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS OF BUSINESS, PROFITS, BUSINESS INTERRUPTION, LOSS OF BUSINESS INFORMATION, SPECIAL, INCIDENTAL, CONSEQUENTIAL, OR RELIANCE DAMAGES, OR OTHER LOSS) ARISING OUT OF THE USE OR INABILITY TO USE THIS CABLETRON PRODUCT, EVEN IF CABLETRON HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. BECAUSE SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES, OR ON THE DURATION OR LIMITATION OF IMPLIED WARRANTIES, IN SOME INSTANCES THE ABOVE LIMITATIONS AND EXCLUSIONS MAY NOT APPLY TO YOU. FDDI Technology Manual iii

5 Notice UNITED STATES GOVERNMENT RESTRICTED RIGHTS The enclosed product (a) was developed solely at private expense; (b) contains restricted computer software submitted with restricted rights in accordance with Section (a) through (d) of the Commercial Computer Software - Restricted Rights Clause and its successors, and (c) in all respects is proprietary data belonging to Cabletron and/or its suppliers. For Department of Defense units, the product is licensed with Restricted Rights as defined in the DoD Supplement to the Federal Acquisition Regulations, Section (c) (1) (ii) and its successors, and use, duplication, disclosure by the Government is subject to restrictions as set forth in subparagraph (c) (1) (ii) of the Rights in Technical Data and Computer Software clause at Cabletron Systems, Inc., 35 Industrial Way, Rochester, New Hampshire iv FDDI Technology Manual

6 Contents Overview PURPOSE OF THIS MANUAL... v WHO SHOULD USE THIS MANUAL... v STRUCTURE OF THIS MANUAL... v RELATED DOCUMENTS... vi Chapter 1 INTRODUCTION FDDI OVERVIEW FDDI FEATURES Bandwidth Transmission Medium Fault Recovery Frame Transmission Media Access Method Chapter 2 FDDI DEVICES FDDI STATIONS FDDI CONCENTRATORS FDDI BRIDGES OPTICAL BYPASS SWITCHES Chapter 3 FDDI PHYSICAL CONNECTIONS FDDI FIBER CONNECTORS MIC Connector Ports FDDI TWISTED PAIR CONNECTORS Twisted Pair Port Pinouts FDDI PORT CONNECTION RULES Chapter 4 FDDI FRAME FORMATS FDDI DATA FRAMES TOKEN FRAMES i

7 Chapter 5 FDDI RING TOPOLOGY DUAL RING WITHOUT TREES DUAL RING WITH TREES WRAPPED RING SINGLE TREE DUAL HOMING Chapter 6 FDDI RING OPERATION STATION INITIALIZATION RING INITIALIZATION Transmitting the First Token Ring Initialization Synchronous Transmission Asynchronous Transmission Token Priorities Restricted/Non-Restricted Token Mode Ring Timing and Latency Maximum Ring Latency Total Transmission Time Token Rotation Timer Token Hold Timer BASIC RING OPERATION The Beacon Process Frame Transmission Ring Fault Recovery OPTICAL BYPASS SWITCH Chapter 7 BRIDGING WITH THE FDMMIM ETHERNET FRAME TYPES Ethernet II Frame Type Ethernet Raw Frame Type Ethernet Frame Type Ethernet SNAP Frame Type FDDI FRAME TYPES FDDI Frame Type FDDI SNAP Frame Type ETHERNET TO FDDI BRIDGING Ethernet II to FDDI SNAP Frame Bridging Raw Frame to FDDI MAC Frame Bridging Frame To FDDI Frame Bridging Ethernet SNAP Frame to FDDI SNAP Frame Bridging FDDI TO ETHERNET BRIDGING Case Case Case Case ii

8 Appendix A ANSI STANDARDS FOR FDDI THE OSI NETWORK MODEL... A-2 STATION MANAGEMENT (SMT)... A-3 SMT Frame Services... A-3 Connection Management... A-4 Ring Management (RMT)... A-5 MEDIA ACCESS CONTROL (MAC)... A-6 PHYSICAL LAYER PROTOCOL (PHY)... A-6 4-Bit/5-Bit Encoding/Decoding Scheme... A-7 Clock Synchronization... A-7 Elasticity Buffer... A-7 PHYSICAL MEDIUM DEPENDANT (PMD)... A-8 Appendix B FDDI SPECIFICATIONS FDDI DESIGN CONSIDERATIONS...B-2 Ring Length...B-2 Drive Distance...B-2 Attenuation...B-3 Number of Stations...B-3 iii

9 PREFACE PURPOSE OF THIS MANUAL Welcome to the FDDI Technology Manual. This manual provides a basic overview of Fiber Distributed Data Interface (FDDI) technology. The objective of this manual is to help Cabletron s customers better understand FDDI concepts and network operation. WHO SHOULD USE THIS MANUAL This manual is intended for users of Cabletron s FDDI products and should be used as a supplement to Cabletron s FDDI User Manuals. STRUCTURE OF THIS MANUAL This manual is organized as follows: Chapter 1, Introduction - Introduces FDDI features and characteristics. Chapter 2, FDDI Devices - Describes FDDI devices and their functions. Chapter 3, FDDI Physical Connections - Describes how FDDI devices physically attach to the ring. Chapter 4, FDDI Frame Formats - Describes FDDI Frame and Token formats. Chapter 5, FDDI Ring Topology - Outlines various FDDI ring topologies. Chapter 6, FDDI Ring Operation - Outlines basic FDDI ring operation including station initialization, the claim token process and basic ring operation. Chapter 7, Bridging with the FDMMIM- Provides a basic overview of bridging with Cabletron s FDMMIM. Appendix A, ANSI Standards for FDDI - Describes the FDDI standards outlined by the ANSI standards committee. Appendix B, FDDI Rules and Specifications - Provides a quick reference for FDDI specifications and network requirements. v

10 PREFACE RELATED DOCUMENTS The American National Standards Institute (ANSI) Accredited Standards Committee (ASC) Task Group X3T9.5 writes all FDDI standards. The ANSI committee consists of representatives from various networking companies. Cabletron is an active member of the ANSI committee and strictly adheres to these standards while designing new products. For additional FDDI information, refer to the following ANSI documents: Station Management (SMT) - ANSI X3.229 Media Access Control (MAC) - ANSI X Physical Layer Protocol (PHY) - ANSI X Multimode Fiber Physical Layer Medium Dependant (PMD) - ANSI X3.166 Single Mode Fiber Physical Layer Medium Dependent (SMF-PMD) - ANSI X3.184 Twisted Pair Physical Layer Medium Dependent (TP-PMD) - ANSI X3T9.5/ Each document describes essential FDDI entities. These entities perform tasks which are essential to the operation of the FDDI network including media access, token passing, and frame generation. vi

11 Chapter 1 INTRODUCTION This chapter introduces Fiber Distributed Data Interface (FDDI) features and describes characteristics that distinguish FDDI from other Local Area Network (LAN) technologies such as Ethernet and Token Ring. FDDI OVERVIEW FDDI is a 100 megabit per second LAN technology that transmits data frames over dual counter-rotating rings. It is an ideal network backbone technology and is typically used to connect lower speed LANs such as Ethernet 10 megabits per second and Token Ring 4/16 megabits per second. FDDI is primarily a fiber optic network that was originally designed to operate over multimode fiber optic cable but has been modified to operate over single mode fiber optic cable, unshielded twisted pair cable, and shielded twisted pair cable. Figure 1-1 is an example of an FDDI network and shows some of its distinguishing features and components. SINGLE ATTACHED STATIONS DUAL ATTACHED CONCENTRATOR PRIMARY RING SECONDARY RING FDDI DUAL COUNTER-ROTATING RING NETWORK DUAL ATTACHED CONCENTRATOR SINGLE ATTACHED CONCENTRATOR Figure 1-1. Typical FDDI Network 1-1

12 INTRODUCTION FDDI FEATURES FDDI s most distinguishing features are directly related to the fiber optic medium. Although twisted pair cable is a valid FDDI transmission medium, it does not match the performance features of fiber and is used primarily as a low cost solution for desktop connections. The fiber optic medium provides a number of advantages over twisted pair including greater transmission distances, fault recovery, and security. The following definitions highlight some of FDDI s most important features. Bandwidth FDDI bandwidth is 100 megabits per second which is considerably faster than Ethernet 10 megabits per second or Token Ring 4 or/16 megabits per second. The increased bandwidth of FDDI is ideal for the transmission of voice, video, or data. Transmission Medium FDDI transmits data frames over a physical medium of multimode fiber optic cable, single mode fiber optic cable, unshielded twisted pair cable, and shielded twisted pair cable. Multimode fiber optic cable and single mode fiber optic cable provide backbone ring connections while unshielded and shielded twisted pair cable provide low cost connections from the fiber backbone to the desktop. Fiber optic cable provides a number of advantages over copper wire, including: Ring Length: The maximum ring length for a dual-ring FDDI network is 100 Kilometers (60 Miles). The maximum ring length for an FDDI network in the wrapped state (single ring) is 200 Kilometers (120 Miles). Number of Stations per Network: FDDI allows up to 500 stations per network. Security: Fiber cables cannot be tapped without disruption to the ring. Immunity from Electromagnetic Interference: Fiber is not affected by electromagnetic interference. 1-2

13 FDDI FEATURES Fault Recovery FDDI has a dual counter-rotating ring topology that provides a primary path for normal operation and a secondary path for fault recovery. If the primary ring fails, FDDI changes the data path to the secondary ring. Frame Transmission FDDI stations communicate on the ring using the following message formats: Frames: provide information concerning ring management, network problems, and statistics. Token: The token is a special frame that controls access to the ring. Only the FDDI station holding the token can transmit data on the ring. Refer to Chapter 4, FDDI Frames for more information about frames. Media Access Method FDDI uses a token passing media access method to transmit frames on the ring. A token is a special frame that circulates around the ring. When an FDDI station needs to transmit data, it captures the token, transmits the data frames, and reissues the token. Only the FDDI station that possesses the token can transmit data. Chapter 6, FDDI Ring Operation describes the claim token procedure. 1-3

14 Chapter 2 FDDI DEVICES This chapter describes devices that are common to an FDDI network. All devices attached to an FDDI ring must comply with The ANSI X3T9.5 Standards outlined in Appendix A. Typical FDDI devices include stations, concentrators, bridges. and optical bypass switches. Figure 2-1 shows various devices attached to an FDDI ring. The following sections provide a description of each of these devices and their network functions. SINGLE ATTACHED STATIONS ETHERNET NETWORK DUAL ATTACHED CONCENTRATOR PRIMARY RING SECONDARY RING FDDI TO ETHERNET BRIDGE FDDI DUAL COUNTER-ROTATING RING NETWORK DUAL ATTACHED STATION (FILE SERVER) DUAL ATTACHED CONCENTRATOR SINGLE ATTACHED CONCENTRATOR Figure 2-1. Devices on an FDDI Ring 2-1

15 FDDI DEVICES FDDI STATIONS FDDI stations are addressable nodes on an FDDI network capable of transmitting, receiving, and repeating information. Workstations, Fileservers, and Printers are examples of FDDI stations. Stations connect to the ring using one of the following configurations: Single-Attachment Station (SAS): connects to one ring. Dual-Attachment Station (DAS): connects to both rings. Figure 2-2 shows each of the station configurations. SINGLE ATTACHED STATION DUAL ATTACHED STATION MAC MAC MAC PHY SMT PMD PHY-A PHY-B SMT PMD-A PMD-B In Out Primary In Secondary Out Secondary In Primary Out Figure 2-2. FDDI Stations 2-2

16 FDDI CONCENTRATORS FDDI CONCENTRATORS FDDI concentrators are central hubs that provide connections to the ring for single attached stations. Concentrators may or may not have a MAC entity and connect to the ring using one of the following configurations: Null-Attachment Concentrator - Does not connect to the Dual Rings. Single-Attachment Concentrator (SAC) - connects to one ring. Dual-Attachment Concentrator (DAC) - connects to both rings. Figure 2-3 shows each of the FDDI concentrator configurations: SINGLE ATTACHED CONCENTRATOR DUAL ATTACHED CONCENTRATOR PMD-3 PMD-2 PMD-1 MAC MAC PMD-3 PMD-2 PMD-1 PHY-3 PHY-2 PHY-1 PHY-3 PHY-2 PHY-1 MAC PHY PHY-A PHY-B SMT PMD SMT PMD-A PMD-B In Out Primary In Secondary Out Secondary In Primary Out Figure 2-3. FDDI Concentrators 2-3

17 FDDI DEVICES FDDI BRIDGES FDDI bridges connect multiple FDDI networks. They also link FDDI rings to similar networks such as Token Ring or Ethernet. Similar networks have the same upper five layers of the OSI model but have different Link and Physical layers. A bridge does not expand an existing FDDI ring, it connects rings. Figure 2-4 is an example of an FDDI bridge configuration. ETHERNET NETWORK FDDI TO ETHERNET BRIDGE FDDI DUAL COUNTER-ROTATING RING NETWORK Figure 2-4. FDDI Bridge Bridges typically use one of two bridging techniques, encapsulation or translation. Translation bridges translate non-fddi MAC layer packets to FDDI data frames. For example, translation bridges allow an Ethernet station to talk to an FDDI station. Encapsulation bridges enclose the non-fddi packets within the FDDI protocol and therefore must be installed in pairs. The sending bridge encapsulates the message and the receiving bridge strips the FDDI protocol, restoring the original frame. The bridge maintains routing information used to filter (prevent frames from crossing the bridge) or forward messages across the bridge. 2-4

18 OPTICAL BYPASS SWITCHES OPTICAL BYPASS SWITCHES Optical bypass switches maintain ring continuity if an FDDI station fails or becomes removed from the ring. This device is inserted between a station and the FDDI ring connection and provides passive optical switching of both the primary and secondary ring cables. For example, if an FDDI station fails, the optical bypass switch automatically diverts FDDI frames through the switch instead of through the station. This prevents a wrap condition on the FDDI ring. Figure 2-5 shows an optical bypass switch and the data paths through the switch in both the bypass and operational (non-bypassed) states. NOTE Optical bypass switches do not connect Singlemode fiber connections to Multimode fiber connections. BYPASS STATE Station Power Off OPERATIONAL STATE Station Power On Station Station FDDI Dual Optical Bypass Switch FDDI Dual Optical Bypass Switch FDDI Ring FDDI Ring Figure 2-5. Optical Bypass Switch 2-5

19 Chapter 3 FDDI PHYSICAL CONNECTIONS This chapter describes FDDI connector types and FDDI connection rules. Multimode fiber and single mode fiber optic cable use Media Interface Connectors (MICs) to attach to FDDI ports while Twisted pair cable attaches to concentrators using RJ45 ports and connectors. The following section describe each connector type. FDDI FIBER CONNECTORS Multimode fiber and singlemode fiber optic cable use Media Interface Connectors (MICs) to attach to FDDI ports. The MIC consists of two halves: a connector and a receptacle. The connector is the male half, which resides on the fiber optic cable. The receptacle is the female half, which resides on the FDDI station. Both the connector and receptacle have keys which ensure proper alignment of the primary and secondary fibers. Figure 3-1 shows each MIC configuration. PRIMARY IN TYPE A SECONDARY OUT Type A DUAL ATTACHMENT SECONDARY IN TYPE B PRIMARY OUT Type B IN TYPE M OUT Type M SINGLE ATTACHMENT IN TYPE S OUT Type S Figure 3-1. Fiber Optic Connectors and Receptacles 3-1

20 FDDI PHYSICAL CONNECTIONS MIC Connector Ports MIC connectors have keys which distinguish port types. Types A, B, and M are precision connectors, mechanically keyed to ensure proper connections to Primary Ring-In and Primary Ring-Out fibers. The Type S connector has a wide, centrally located key and is considered a non-precision connector for use at the station end of a Single Attachment Station lobe cable. The following list describes each port s function on the FDDI ring: A ports - receive data from the Primary ring, and transmit data to the Secondary ring. Type A ports provide dual attachment to the primary and secondary data paths of the main ring. B ports - receive data from the Secondary ring, and transmit data to the Primary ring. Type B ports provide dual attachment to the primary and secondary data paths of the main ring. M (Master) ports - receive and transmit data from same ring. Type M ports are used for single attachment stations and concentrators. S (Slave) ports - receive and transmit data from same ring. Type S ports are used for single attachment stations and concentrators. 3-2

21 FDDI TWISTED PAIR CONNECTORS FDDI TWISTED PAIR CONNECTORS The Twisted Pair Physical Layer Medium Dependent (TP-PMD) ANSI specification is a working draft and many of the standards proposed by the TP-PMD have not been approved by the networking industry. The twisted pair specifications listed in this document are specific to Cabletron only. Cabletron s FDDI products use twisted pair cabling to connect Single Attached Stations to FDDI concentrators. Twisted pair cable does not replace fiber cabling on the dual backbone ring. Twisted pair configurations use the following port types: M (Master) ports - receive and transmit data from same ring. Type M ports are used for single attachment stations and concentrators. S (Slave) ports - receive and transmit data from same ring. Type S ports are used for single attachment stations and concentrators. Twisted Pair Port Pinouts To connect a Type M concentrator port to a Type S station port the twisted pair cable must be crossed over. Figure 3-3 shows the pinouts for a twisted pair port. Pin 1 RJ-45 TP-PMD PORT Contact Signal Transmit + Transmit N/A N/A N/A N/A Receive + Receive Caution: Ground only one end of an STP segment. For Cabletron TP-PMD products, the port casing is grounded. Figure 3-2. Pinouts for an FDDI RJ45 Port 3-3

22 FDDI PHYSICAL CONNECTIONS FDDI PORT CONNECTION RULES In a typical FDDI ring, the following rules apply: A ports should only connect to B ports. B ports should only connect to A ports. M ports should only connect to S ports. All other port-to-port connections are either Illegal or Undesirable because they may result in unexpected ring topologies. The Station Management entity checks for Illegal or Undesirable connections when any link is established. If the connection is Illegal, then the connection is automatically dropped. If the connection is Undesirable, allowance of the connection is up to the Connection Policy of connection nodes. A primary functions of the Station Management entity is to control physical connections among A, B, M, and S type ports. Table 3-1 summarizes the FDDI connection rules. Table 3-1. FDDI Connection Rules Port 2 A B S M P o r t 1 A V,U V V,U V,P B V V,U V,U V,P S V,U V,U V V M V V V X V - valid connection X - illegal connection U - undesirable connection P - valid, but when both A and B are connected to M ports, only the B connection is used. Connecting A and B to M ports creates a dual homing configuration. Dual homing is a method of configuring concentrators with a redundant topology. 3-4

23 Chapter 4 FDDI FRAME FORMATS This chapter describes FDDI frame formats. The MAC entity generates two basic message formats, Tokens and Frames. The following sections describe each message format. FDDI DATA FRAMES Figure 4-1 shows the overall format of an FDDI Token and Data frame: TOKEN Preamble 16 Symbols Starting Delimiter 2 Symbols Frame Control 2 Symbols Ending Delimiter 2 Symbols FRAME J K T T Frame Check Sequence Coverage T Preamble 16 Symbols Starting Delimiter 2 Symbols Frame Control 2 Symbols Destination Address 4 or 12 Symbols Source Address 4 or 12 Symbols Information 0 Symbol Pairs Frame Check Sequence 8 Symbols Ending Delimiter 1 Symbol Frame Status 3 Symbols Maximum symbols Figure 4-1. FDDI Frame Formats 4-1

24 FDDI FRAME FORMATS Table 4-1. FDDI Data Frame Layout Field Name Field Size Field Definition Preamble 16 + symbols Signals the start of a valid frame. Start Delimiter 2 Symbols Signals that FC is next field. Frame Control 2 Symbols Identifies the type of frame (MAC, LLC, etc.). Destination Address 4 or 12 Symbols Source Address 4 or 12 Symbols Information (Data) 8956 Symbols Address of the destination of the packet. Address of the packets origin. Contains the data to be transferred. FCS (Frame Check Sequence) ED (Ending Delimiter) 8 Symbols Used to determine integrity of the packet. 1 Symbol Signals the end of the frame. FS (Frame Status) 3 Symbols Indicates the status of the frame. NOTE FDDI uses a 5 bit symbol scheme. The PHY handles the encoding and decoding of the four bit to five bit symbols. 4-2

25 TOKEN FRAMES TOKEN FRAMES The Token is made up of 22 symbols. Table 4-2 explains each of the Token Frame fields. Table 4-2. FDDI Frame Type Field Name Field Size Field Definition Preamble 16 + symbols Maintains clock synchronization Start Delimiter Frame Control ED (Ending Delimiter) 2 Symbols Signals the start of a valid token. 2 Symbols Distinguishes a Token from a Frame. 1 Symbol Signals the end of the Token. 4-3

26 Chapter 5 FDDI RING TOPOLOGY This chapter describes FDDI ring topologies as well as FDDI design considerations that may be useful to a network designer. DUAL RING WITHOUT TREES The Dual Ring Without Trees configuration consists of dual attachment stations that form a ring by connecting A ports to B ports and B ports A ports. This configuration is commonly used in small engineering/research environments to localize FDDI rings. The disadvantage of the Dual Ring Without Trees configuration is the risk of a wrap condition in the event of a station failure. Optical bypass switches are typically used in this configuration to prevent a wrap condition. Figure 5-1 shows a Dual Ring Without Trees configuration. DUAL ATTACHED STATION PRIMARY RING SECONDARY RING FDDI DUAL COUNTER-ROTATING RING NETWORK DUAL ATTACHED STATION Figure 5-1. FDDI Dual Ring Topology 5-1

27 FDDI RING TOPOLOGY DUAL RING WITH TREES A Dual Ring with Trees configuration uses dual attachment concentrators, single attachment concentrators, and single attachment stations to form tree structures. Single attachment stations and single attachment concentrators connect to the dual attachment concentrator M ports instead of the ring. This configuration enhances network reliability because dual attachment concentrators automatically reconfigure the network each time stations are inserted or removed from the ring. Another advantage of the Dual Ring with Trees configuration is cost. Adapter boards for single attachment stations are cheaper than adapter boards for dual attachment concentrators. Figure 5-2 shows a typical Dual Ring with Trees configuration. SINGLE ATTACHED STATIONS DUAL ATTACHED CONCENTRATOR PRIMARY RING SECONDARY RING FDDI DUAL COUNTER-ROTATING RING NETWORK DUAL ATTACHED CONCENTRATOR SINGLE ATTACHED STATIONS SINGLE ATTACHED CONCENTRATOR TREE STRUCTURE Figure 5-2. FDDI Dual Ring of Trees 5-2

28 WRAPPED RING WRAPPED RING A Wrapped Ring is the result of a broken cable or a faulty Dual Attachment Concentrator or Dual Attachment Station. Figure 5-3 shows a cut cable between concentrator 3 (downstream neighbor) and concentrator 4 (upstream neighbor). Both Concentrator 3 and Concentrator 4 wrap. This scenario repeats for a failed station or concentrator. Both the upstream and downstream neighbors wrap. When a Dual Attachment Concentrator or Dual Attachment Station wraps a port, it internally connects the primary ring to the secondary ring. This maintains a data path for frame transmission by creating one contiguous enveloped ring. Similarly, if a Dual Attachment Station or Dual Attachment Concentrator is powered off or removed from the ring, the upstream and downstream neighbors wrap. RING WRAP DUAL ATTACHED CONCENTRATOR 3 CABLE FAILURE PRIMARY RING A B DUAL ATTACHED CONCENTRATOR 4 B SECONDARY RING A A FDDI DUAL COUNTER-ROTATING RING NETWORK B DUAL ATTACHED CONCENTRATOR 2 B A DUAL ATTACHED CONCENTRATOR 1 Figure 5-3. Wrapping a Broken Ring 5-3

29 FDDI RING TOPOLOGY SINGLE TREE The Single Tree topology does not use the dual ring, only the single ring. All of the network devices are single attachment stations and single attachment concentrators. Since the Single Tree topology only uses the single ring, there is no back up path if a cable fails. If an individual single attachment station fails, it does not affect the rest of the network. If a single attachment concentrator fails, the single attachment stations become separated from the rest of the network. Figure 5-4 shows a Single Tree topology. SINGLE ATTACHED STATIONS SINGLE ATTACHED CONCENTRATOR Figure 5-4. FDDI Tree Topology DUAL HOMING Dual Homing provides redundant paths to critical network devices such as fileservers, bridges or workstations. This configuration requires the following: The FDDI network must be a Dual Ring With Trees. The critical device must be a Dual Attachment Station. The critical device must attach to Dual Attachment Concentrators. Figure 5-5 illustrates a Dual Homing configuration. The Dual Attachment Station connects to the M ports of two different Dual Attachment Concentrators. FDDI connection rules considers this an Undesirable connection, but the Station Management entity allows the B to M port connection to be active while the A to M port connection remains in standby. This creates a redundant data path for the critical network device. If for any reason the B to M connection is lost, the Station Management entity switches the data path to the A to M connection. This protects the critical network device from a failure on either Concentrator. 5-4

30 DUAL HOMING FDDI DUAL ATTACHED STATION FILESERVER DUAL ATTACHED CONCENTRATOR 3 DUAL HOMED CONNECTION PRIMARY RING SECONDARY RING FDDI DUAL COUNTER-ROTATING RING NETWORK DUAL ATTACHED CONCENTRATOR 2 DUAL ATTACHED CONCENTRATOR 4 DUAL ATTACHED CONCENTRATOR 1 Figure 5-5. Dual Homing Topology 5-5

31 Chapter 6 FDDI RING OPERATION This chapter describes basic FDDI ring operation, including: Station Initialization Ring Initialization Proper operation of the FDDI ring requires interaction between the Station Management (STM), Media Access Control (MAC), Physical Layer Protocol (PHY), and Physical Layer Media Dependent (PMD) entities. The Station Management entity is responsible for coordinating station initialization and the normal operation of the FDDI ring. Refer to Appendix A for more information concerning FDDI entities. STATION INITIALIZATION When a station attaches to the ring, it must run an initialization procedure. The station initialization procedure checks the integrity of the fiber optic link and determines if the ports on each station are ready to exchange data. Station initialization is a function of Physical Connection Management (PCM), which is a subentity of Station Management. Figure 6-1 shows a new station attaching to the ring. The Station Initialization procedure begins when the new station sends signals to the PCM entity of the downstream station. The PCM entities of each station then begins the station initialization procedure, which begins when the Physical Layer Protocol detects an active fiber optic link. The following sections explain each test. 6-1

32 FDDI RING OPERATION STATION C STATION B MAC PHY B PHY A Link C/A Link B/C Link A/B PHY B PHY A MAC PHY A PHY B MAC STATION A Figure 6-1. FDDI Station Initialization 6-2

33 STATION INITIALIZATION Table 6-1 explains the station initialization procedure. Table 6-1. Station Initialization Break State Sequence Quiet Line State Description Figure 6-1 shows the PCM of station C entering the Break State. During the Break State, Station C sends Quiet Symbols to the PHY in station B. As a result, Station B stops transmitting any data or symbols and enters the Break State. During the Break State, Station B breaks all existing connections and enters the Quiet Line State. In the Quiet Line State, both stations send Quiet Symbols to each other. The Quiet Line State means that the stations have each other s attention to continue with the initialization sequence. Note: If Station B had not entered into the Quiet Line State, then Station C would have returned to the Break State. Connect State During the Connect State each station sends a continuous stream of Halt Symbols. Halt Symbols synchronize the clocks in each station. Halt State Next State/Signal State Idle Line State After both stations have had enough time to synchronize clocks, they enter the Halt State then proceed to the Next State. The Next State, in conjunction with the Signal State, allows the two stations to exchange port information (A, B, S, or M type ports) and port compatibility (S to M, or A to B, etc.). Note: These two states are also used to exchange information concerning the Link Confidence Test of the physical connection and MAC. The Idle Line State is used for transitions between the Next State and the Signal State. When it is ready to receive information, a station sends continuous Idle Symbols to its neighbor. If Station C were to enter into the Next State first, it would send Idle Symbols to station B. Station B would then enter the Signal State. This particular exchange of information is accomplished by using Halt Symbols and Master Symbols (alternating Halt and Quiet Symbol Pairs). The reception of either Halt Symbols or Master Symbols for more than 30µs causes the receiving station to enter either the Halt Line State or the Master Line State. The Halt Line State indicates that the received bit was a 1, while the Master Line State indicates a 0. The type A port is identified as 00 which means that the receiving station would record two Master Line States. The type B port is identified as 01, which would indicate a Master Line State followed by a Halt Line State. 6-3

34 FDDI RING OPERATION Table 6-1. Station Initialization Link Confidence Test Join State Sequence Description Link Confidence Test information is also exchanged between stations. This information indicates the length of the test and determines if a MAC is involved. If a MAC is not involved in the test, Idle Symbols are transmitted during the Link Confidence Test. When there is a MAC involved in the test, then frames are transmitted as well as procedures to test frame transmission and reception and token passing and MAC recovery processes. If the stations pass the Link Confidence Test then the stations continue to the Join State. The Join State ensures that both stations reach the Active State together. A sequence of line states is used to get the station from the Join State to the Active State. The detection of Halt Symbols causes the station to enter the Join State. Detection of Master Symbols cause the station to enter the Verify State. finally, the reception of Idle Symbols causes the station to enter the Active State. Once the PCM has reached the Active State, it will send a signal to Configuration Management to join the station to the ring as shown in Figure 6-2. RING INITIALIZATION STATION C STATION B MAC PHY B PHY A Link C/A Link B/C Link A/B PHY B PHY A MAC PHY A PHY B MAC STATION A Figure 6-2. The Joint State 6-4

35 RING INITIALIZATION After the Station Initialization process is complete and the stations are physically attached to the ring, as shown in Figure 6-3, the ring must be initialized. The Ring Initialization procedure determines which station transmits the first token. It also sets the Operational Token Rotation Time. The Operational Token Rotation Time determines how long a station must wait before it receives a token. This process guarantees that each station has a chance to transmit frames onto the ring within a specific time period. STATION C STATION B MAC PHY B PHY A Link C/A Link B/C Link A/B PHY B PHY A MAC PHY A PHY B MAC STATION A Figure 6-3. All Stations Physically Attached to the Ring 6-5

36 FDDI RING OPERATION Transmitting the First Token Stations on an FDDI ring bid for the right to issue the first token. Each station has a preset timing requirement called a Token Rotation Timer (TRT). The TRT determines how often the token must visit the station. This time is compared with the timing requirements of the other stations on the ring and the stations bid for the Target Token Rotation Time (TTRT). The station with the lowest TRT wins the right to issue the first token. The bidding procedure begins when each station generates a Claim Frame. This is a special Frame that includes the sending station s address and TRT. Each station compares its own TRT to the TRT on the Claim Frame. If the station s TRT is lower than the Claim Frame, then it discards the Frame and issues its own Claim Frame. If the station s TRT is higher than the Claim Frame then it repeats the Claim Frame. Eventually, the Claim Frame with the lowest TRT remains on the ring and the station that issued the Claim Frame with the lowest TRT issues the first token. It is this station that is then allowed to initialize the ring with its winning bid. The winning bid value becomes the operational Token Rotation Time (T_OPR) for the ring. Ring Initialization Ring Initialization ensures that each station on the ring has the same TRT. This is done by each station setting their T_OPR to the winning bid value and setting its Token Rotation Timer (TRT) to the same value. The winning bidder will transmit the bid around the ring. During this time use of the ring is restricted until all the stations receive the value of T_OPR. At the completion of this operation a nonrestricted token is issued. During the second token rotation each station accumulates the current synchronous bandwidth from the Token Rotation Timer (how long it took for the token to circulate the entire ring). Once the synchronous bandwidth has been calculated and divided between all stations, the remaining bandwidth can be used for asynchronous transmissions. 6-6

37 RING INITIALIZATION Synchronous Transmission Transmission of normal Protocol Data Units is controlled by a Timed Token Rotation Protocol. This protocol supports two classes of service, synchronous and asynchronous. Synchronous service gives each station a guaranteed bandwidth and response time. Each station can be assured that they see a token once every 2 x T_OPR (two times the winning TTRT bid). It is therefore good for those applications whose bandwidth and response time limits are predictable in advance, permitting them to be pre-allocated via station management. The time budget allowed for transmission is limited to ensure fairness between all stations. The bandwidth allocation process in Station Management sets this maximum transmission time and is a percentage of the total time allocated for synchronous transmission. Asynchronous Transmission This type of service is used for those applications whose bandwidth requirements are less predictable (e.g. bursty or potentially unlimited) or whose response time requirements are less critical. Asynchronous bandwidth is instantaneously allocated from a pool of remaining bandwidth. Transmission time is not guaranteed but is related to the activity of all the stations on the ring. Once transmission has started, the time a station is allowed to transmit is limited to the value of a timer called the Token Holding Timer (THT). There is a two tier allocation mechanism for controlling Asynchronous bandwidth which is achieved by using two classes of tokens Restricted an Nonrestricted Tokens. Token Priorities Different priority levels can be set within the asynchronous transmissions depending on the value of TRT when the token is received. Within each station, the MAC transmitter maintains a Token-Rotation Timer (TRT) to control the ring scheduling. TRT is reset each time a token arrives. A token arriving at a station before the TRT reaches the T_OPR value is called an Early Token. An early token can be used for either Synchronous or Asynchronous transmission. A token arriving after TRT reaches the value of T_OPR is known as a Late Token and this type of token can only be used for Synchronous transmission. Different mechanisms may be used to limit the length of a station s transmission whether it be Synchronous or Asynchronous, but in no case should the station hold the Token longer than the negotiated Token Holding Timer (THT). 6-7

38 FDDI RING OPERATION Restricted/Non-Restricted Token Mode Asynchronous bandwidth is controlled by a two tier allocation mechanism, enforced by two classes of tokens. Normal operation is achieved using a Non-Restricted Token being issued by a station. Restricted Token Mode may be entered when a station wishes to initiate an extended dialogue requiring substantially all of the unallocated ring bandwidth (e.g., an extended burst data transfer from a high speed device). If a station receives a non-restricted token that is very early it can transmit the initial part of an extended dialogue to the assigned destination station and it will then issue a restricted token. The destination station receives the initial dialogue and will enter restricted token mode. When the restricted token arrives at this station now, it can reply and then issue a restricted token. Both stations can now exchange frames and restricted tokens for the duration of the dialogue (this could typically be many times the negotiated T_OPR value). Restricted Token mode is terminated when a station captures a restricted token, transmits its final dialogue frame(s) and then issues a non-restricted token. Since fairness is the name of the game within the FDDI protocol, there is no need to use a Token Holding Timer for the extended dialogue. However the Station Management entities negotiate and monitor a maximum restricted Token mode time. If restricted Token mode operation exceeds this time, SMT should abort the extended dialogue. The advantage of using Restricted token mode is that it is fair to all stations on the ring. Each station on the ring that requires an extended dialogue has an opportunity to do so. Ring Timing and Latency Transmission has to be guaranteed under synchronous operation and the protocol ensures that the right to transmit will occur by twice the negotiated T_OPR value. To achieve this, the ring latency (the propagation delay of transmitted data around the ring) and the total transmission time by the stations must be limited. Maximum Ring Latency 6-8 The maximum ring latency is the maximum delay introduced into the ring by each of the stations and the cable that makes up the physical ring. This delay can be calculated using the maximum allowable rules that are stated within the FDDI specification. The maximum ring distance (allowing for a ring in the wrapped state) is 200 km. and the maximum number of connections allowed on this ring is The maximum ring latency equals ms (this is the default in the FDDI specification). The formula for Maximum Ring Latency is: Maximum Ring Latency = Total Station Delay + Total Fiber Delay.

39 BASIC RING OPERATION Total Transmission Time The total allowable transmission time is the negotiated value of T_OPR minus the maximum ring latency. The formula for Total Transmission Time is: Total Transmission Time = T_OPR - Maximum Ring Latency. Token Rotation Timer Each station has a timer called the Token Rotation Timer (TRT) that is used to control ring scheduling during normal operation and to detect and recover from serious ring error situations. TRT is initialized with different values during different phases of ring operation. Whenever TRT expires, it is reinitialized to the current value of T_OPR. Token Hold Timer Each station has a timer called the Token Hold Timer (THT) that controls how long the station is allowed to transmit asynchronous frames. THT is initialized with the current value of TRT when a token is captured. BASIC RING OPERATION Once the stations have completed all their self tests the Station Management works with the Physical Layer Protocol (PHY) and the configuration logic to connect adjacent PHY entities and perform a handshake by the transmission of line state symbols as previously discussed. If the links are good, then the mini rings are joined until a fully configured ring is achieved. Once the ring is established, stations take part in the Claim Process as previously discussed. As a result of this process, the station bidding the lowest the Target Token Rotation Time initializes the ring by issuing a non-restricted token. Once this token has been released other station on the ring can begin the transmission of frames. 6-9

40 FDDI RING OPERATION The Beacon Process The Beacon process is used to recover from serious ring faults. These faults include a failed Claim Process, a broken ring, re-configured ring, or the joining of two logical rings into one. The purpose of the Beacon Process is to signal to all other stations that a significant logical break in the ring has occurred and to provide diagnostics or other assistance to recover the ring using SMT. Upon entering the Beacon state a station continuously transmits MAC Beacon frames to it s downstream neighbor. All stations on the ring repeat Beacon Frames so there comes a time when the only station beaconing is the station downstream from the logical break. While the beaconing process is operating the Connection Management portion of SMT will have noticed a loss of link at the PHY level and hence will have no line activity. Connection Management informs Station Management and then sends control symbols around the ring to its upstream neighbor (it already knows this address as the upstream neighbor because all stations transmit special MAC frames called Neighbor Information Frames (NIF) to their downstream MACs on a periodic basis). The station on the other side of the break receives the beacon frames and under control of SMT removes from the ring to perform local tests. If these tests pass, it re-enters the ring. The beaconing station still has not seen its own frames returned, so it removes itself from the ring and perform some basic tests. With the satisfactory completion of these tests, Station Management will force the relevant connections into the Wrap state. Both the primary and the secondary rings will now be used to recover the ring and the beaconing station will receive its beacon frames back. Once the beaconing station receives the transmitted frames, it knows the ring is now re-configured and the initialization process can begin. Frame Transmission When an FDDI node needs to transmit a frame onto the ring it must first capture the Token as it enters the node, The node transmits the frame(s) onto the ring and then transmits the Token. The frame will circulate around the ring, being repeated by each node, until it reaches the destination node, This node recognizes the frames s destination address and copies the frame into its receive buffer; and then repeats the frames back onto the ring, The frame will continue to circulate the ring and then is stripped from the ring by the originating node. 6-10

41 BASIC RING OPERATION Ring Fault Recovery An FDDI network consists of two distinct separate rings., the primary ring and the secondary ring. Under normal conditions data frames travel on the primary ring and the secondary ring is used as a back-up path. If a fiber is cut between two Dual Attached nodes its upstream and downstream neighbor will wrap. When a node wraps a port it internally connects the primary ring to the secondary ring. This maintains a data path for frame transmission by effectively creating one contiguous enveloped ring. Similarly, if a Dual Attached node is de-powered or de-inserted, the upstream and downstream neighbors will wrap. Since FDDI networks employ a ring topology, the entire network is vulnerable to the frailties of each ring segment and failures of the individual stations. The ring of trees topology reduces the risk of a single node bringing the entire network down. To further reduce this vulnerability, a redundant data path is provided in the main ring trunk cabling. In theory, the ring topology requires media that is capable of only one-way traffic to achieve the circular flow of data. In practice, an FDDI ring uses media that provides two fiber optic ring paths, a primary ring and a secondary ring. The secondary ring is used to restore the continuity of the ring in the event of a failed node or trunk segment (broken trunk cable). Figure 6-4 shows how the open ends of the primary ring are wrapped into the secondary ring, restoring continuity through the creation of a new ring. RING WRAP DUAL ATTACHED CONCENTRATOR 3 CABLE FAILURE PRIMARY RING A B DUAL ATTACHED CONCENTRATOR 4 B SECONDARY RING A A FDDI DUAL COUNTER-ROTATING RING NETWORK B DUAL ATTACHED CONCENTRATOR 2 B A DUAL ATTACHED CONCENTRATOR 1 Figure 6-4. Wrapping a Broken Ring 6-11